The present invention relates to a fluid power cylinder cushioning system and, more particularly, to a system for adjusting and accurately controlling the speed of a fluid piston as it approaches the ends of the cylinder.
In fluid power piston cylinders cushioning systems have been provided in the past for cushioning the cylinder against the shock and vibration which might otherwise occur as the piston in the cylinder reaches the end of its stroke adjacent the end closures of the cylinder. These prior cushioning systems have included the use of restrictive check valves for permitting the full flow of fluid to drive the piston in one direction, but restrict the flow of fluid toward the end of the piston stroke in the other direction. Other cushioning systems have also employed flapper seals. Still other systems have employed adjustable fluid bypass valves in combination with circular seals about the piston rod. In these latter mentioned systems, the circular seals are actuated by an actuating mechanism on the piston to seal the fluid passages against the flow of fluid from the space between the piston and the cylinder end closure as the piston moves toward the end, and the discharge of fluid from the space is adjustably throttled through the fluid bypass. When the piston is to be moved in the opposite direction, the seal is unseated to permit a less restrictive flow of fluid to the space between the piston and the cylinder end closure.
Each of these prior cushioning systems suffer shortcomings.
The use of restrictive check valves and flapper seals results in a complex assembly which is relatively expensive and difficult to machine and assemble.
Once sealing and cushioning have been completed, it is important that the restriction to fluid flow in the opposite direction be rapidly and substantially completely eliminated in order to reverse the motion of the piston. In the prior systems incorporating circular seals which are actuated by actuating mechanisms on the piston, the seals are generally somewhat reduced in diameter to permit such rapid elimination of restriction to fluid flow and the unrestricted flow of fluid about the perimeter of the seals to reverse the piston. As a result, the seals are subject to damage and early wear because they can not be maintained in a centered condition with respect to the actuating mechanism on the piston. Because such actuating mechanisms typically move into and out of the seal, they tend to damage the seal during operation if the seal is not centered.
Another difficulty in the last mentioned cushioning systems which also employ needle throttling valves in a bypass, is the inability to accurately machine the valves and their valve seats to the extremely small clearances necessary to achieve a high degree of adjustability. This is particularly true in small power cylinders where the throttling valve needles have to be machined to tolerances of 5-ten thousandths of an inch or less to achieve quality cushioning adjustment, i.e. machined essentially to watchmaker fits.
A fluid power cylinder cushioning system incorporating the principles of the present invention overcomes the aforementioned shortcomings. In cushioning systems incorporating the principles of the present invention, a seal is provided which is capable of rapid actuation to both seal and unseal the fluid flow passages, which is inexpensive and easy to assemble, which rapidly permits the substantially unrestricted flow of fluid when needed, and which may be maintained in a centered condition at all times with respect to the actuating mechanism on the piston, thus substantially reducing damage and wear to the seal. Also in a cushioning system incorporating the principles of the present invention, a method has been discovered in which the tolerances and clearances of the throttling valve and its valve seat may be easily and inexpensively formed with a substantially zero clearance, thus permitting a highly precise and readily adjustable throttling range over which the cushioning system may operate.
In one principal aspect of the present invention, a cushioning system for a fluid power cylinder comprises a first passage in an end cap closure which communicates with the space between the end cap closure and the piston for the flow of fluid to and from the space, and a second passage communicating with the space for the flow of fluid from the space. Throttling means throttles the fluid which flows from the space through the second passage. A resilient seal in the first passage has an opening therein and a plurality of projections spaced from each other and extending in a direction opposite the opening. The projections permit the flow of fluid past the seal and center the seal in the first passage. Seal actuating means on the piston actuates the seal when in the opening of the seal and in response to the movement of the piston toward the end cap closure to cause the seal to substantially seal the first passage against the flow of fluid therethrough from the space.
In another principal aspect of the present invention, the aforementioned seal comprises an O-ring, and the projections extend radially outwardly from the O-ring.
In still another principal aspect of the present invention, the aforementioned seal actuating means extends from the piston in a direction substantially parallel to the direction of movement of the piston and is positioned to move into and out of the opening in the seal. The projections center the seal and its opening relative to the seal actuating means when the seal actuating means is out of the opening.
In still another principal aspect of the present invention, the aforementioned seal actuating means actuates the seal upon entry into the opening to substantially seal the first passage as the piston moves toward the end cap closure, and permits deactivation of the seal to allow substantially unrestricted flow of fluid past the seal to move the piston away from the end cap closure.
In still another principal aspect of the present invention, the piston rod of the piston extends through the opening in the seal, and the seal actuating means comprises an enlargement on the piston rod.
In still another principal aspect of the present invention, retaining means retains the seal in the first passage. The retaining means has an opening overlying the opening in the seal and receives the seal actuating means. The retaining means also includes a plurality of spaced projections extending away from its opening, the space between the projections of the retaining means being greater than the width of the projections on the seal.
In still another principal aspect of the present invention, the aforementioned second passage includes a wall, and the throttling means comprises a valve having a longitudinally extending portion which is moveable from a first position to seal the second passage by engaging the passage wall to any one of a plurality of second positions relative to the passage wall to selectively adjust the flow of fluid through the second passage. The spacing between the longitudinally extending portion of the valve and the passage wall is of substantially zero clearance when the valve is in the first position.
In still another principal aspect of the present invention, a method of forming a valve seat of substantially zero clearance with the valve comprises forming a passage having a first width in a material of a given hardness, deforming at least a portion of the passage to decrease the width of the passage at said portion, and inserting a valve having a given shape and width and a hardness greater than the given hardness into said portion of the passage to form the decreased width portion of the passage to conform substantially identically to the given shape and width of the valve, whereby the clearance between the valve and the portion of the passage formed by the valve is substantially zero.
In still another principal aspect of the present invention, the aforementioned method includes forming a second passage having a width greater than and extending from the first passage, and the transition between the first and second passages is defined by a shoulder. The shoulder is deformed to deform the first mentioned passage portion to decrease its width.
In still another principal aspect of the present invention, the aforementioned methods include forming the first mentioned passage adjacent its transition to decrease the width of the first passage with a punch, removing the punch, and inserting the valve into the decreased width portion of the first passage to further deform the decreased width portion to conform substantially identically to the given shape and width of the valve.
These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.